Currently, mobile communication service may be classified into asynchronous service, widely adopted in Europe, and synchronous service, widely adopted in North America. Further, as a new standard of mobile communication technology for transmitting packets at high speed, International Mobile Telecommunications (IMT)-2000 service has been developed in North America and Europe.
The synchronous IMT-2000 service has been developed into Code Division Multiple Access (CDMA) 2000 1x and CDMA2000 1x Evolution Data Only (EV-DO), and the asynchronous IMT-2000 service has been developed into Wideband CDMA (WCDMA) Universal Mobile Telecommunications System (UMTS) service. In this service environment, a dual band/dual mode terminal (DB/DM mobile communication terminal) capable of being used both in a synchronous mobile communication system and in an asynchronous mobile communication system has been developed so as to support global roaming between a synchronous mobile communication network and an asynchronous mobile communication network. With such a mobile communication terminal, different services can be used in the respective areas of an asynchronous system and a synchronous system.
Currently, the asynchronous mobile communication network is being constructed for regions having great demand for service and, therefore, the synchronous mobile communication network is evolving such that the service area thereof includes the service areas of asynchronous systems. In this environment, handover between the systems is required to provide continuous service in the case where a user moves between the asynchronous mobile communication network and the synchronous mobile communication network.
Currently, at the time of handover between an asynchronous mobile communication network and a synchronous mobile communication network, the handover is performed in such a way as to stop communication with a connected mobile communication network and then connect to another mobile communication network. In this case, there is a disadvantage in that a long handover time is required, so that a call disconnection occurs for an excessive time, thereby degrading service quality.